Study links low-carb intake with overweight, obesity

PHILADELPHIA — The likelihood of being overweight or obese is heightened significantly for individuals who consume a low-carbohydrate diet, according to recently published research.

The findings, "Carbohydrate Intake and Overweight and Obesity among Healthy Adults," were published in the July issue of the Journal of the American Dietetic Association.

The researchers found that among healthy adults the lowest risk of becoming overweight or obese "may be obtained by consuming 47% to 64% energy from carbohydrates."

The study was published by a team led by Anwar Merchant, a nutritional epidemiologist at McMaster University in Hamilton, Ont.

Rather than judging whether one weight loss diet works better than another, as several studies have inconclusively attempted in recent years, the researchers looked at the eating habits of a large number of healthy adults. Based on those eating habits, they determined that the risk of being overweight was lower for those who were not in the lowest quartile for carbohydrate intake.

Participants in the study were respondents to the Canadian Community Health Survey, Cycle 2.2, which the researchers described as a "cross-sectional representative sample of free-living Canadians" in 2004. The researchers whittled down the 35,107 participants in the study to 20,197 who were adults and then to 11,838 with measured heights and weight. Excluding respondents with highly unusual diets (consuming fewer than 560 calories per day or more than 6,000) and those with health conditions such as cancer or diabetes, the study analyzed 4,451 healthy Canadians for the study.

Diet was assessed in the study using a 24-hour dietary recall method developed by the U.S. Department of Agriculture. About a third of the subjects were administered the dietary recall questionnaire for a second randomly chosen day.

Adjustments in the results were performed for total energy intake, age, leisure time energy expenditure, gender, smoking, education and income adequacy.

Participants in the highest carbohydrate intake category were more likely to be younger, female, never smokers and with individuals with lower income versus those in the lowest intake group.

"Participants in the highest carbohydrate intake category had lower intakes of total calories, protein and fats but more fiber than those in the lowest carbohydrate intake category," the researchers said. "Sugar intake increased with higher carbohydrate intake, 46 grams per day, versus 103 comparing extreme carbohydrate intake."

Overweight and obesity prevalence was 65% in the lowest quartile of carbohydrate intake, 54% in quartile 2, 51% in quartile 3 and 51% in quartile 4.

"Carbohydrate intake and overweight and obesity were inversely related after multivariate adjustment," the researchers said.

While a compelling inverse association was found between carbohydrate intake and the likelihood a subject was overweight, no such conclusions could be reached about associations with fat consumption or intake of particular foods such as vegetables.

"Intakes of fiber, protein, total fat or its subtypes were not associated with risk of overweight or obesity," the researchers said. "Intake of total fruit, vegetables, salad, carrots, potatoes, other vegetables and fruit juices were not associated with overweight or obesity."

To understand the association between carbohydrate intake and overweight/obese among individuals who are not actively trying to lose weight the researchers further analyzed the data by excluding subjects on high-protein or high-carbohydrate diets. They also looked at the data excluding subjects who were obese. In all cases higher carbohydrate intake still was inversely associated with overweight and obesity.

Elaborating on the importance of the study, the researchers noted that overweight and obesity are risk factors for cardiovascular disease.

They noted that participants in the study on average ate less fiber, 13 grams to 22 grams per day, than the 38 grams recommended for men and 25 grams for women and more saturated fat than recommended.

"Thus, efforts to increase fiber and reduce saturated fat intakes, perhaps by avoiding energy dense foods, may provide important health benefits for this population," the researchers said. They went on to suggest the population may benefit from consuming more whole grain rather than refined grain, fewer calories and increasing physical activity.

Citing limitations of their study, the researchers noted the data provided no information on carbohydrate type — simple versus complex. Additionally, because only leisure time exercise was assessed, they lacked data on physical activity associated with work. They also noted the drawback of a 24-hour recall survey as the basis for gathering data.

"Ten days or more of data are usually needed to get accurate estimates of usual intake from 24-hour dietary recalls," they said. They noted a number of steps they took to overcome this limitation, including the follow-up call with a third of participants and asking questions such as whether intake in the previous 24 hours was more or less than usual.

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